Method and apparatus of improving quality of calls in mobile communication system

ABSTRACT

A method and apparatus is provided that improves the quality of voice calls in a mobile communication network. The method of performing transmission/reception of signals in an evolved Node B (eNB) of a mobile communication system includes: receiving a first message including service request information from user equipment (UE); transmitting a second message including the service request information to an Mobility Management Entity (MME); receiving a third message including context information for the UE from the MME; and determining an inactivity timer value for the UE based on the context information. The method and apparatus can maintain, when a voice call is created, connection with calling UE from when the called UE answers the call until the call is set up, thereby preventing part of a caller&#39;s voice data from being lost.

TECHNICAL FIELD

The present invention relates to a method of improving the quality ofvoice calls in a mobile communication network that prevents part ofvoice data from being lost right after the call is established.

BACKGROUND ART

Mobile communication systems have been developed to provide voice callservices, supporting users' mobility. With the development ofcommunication technology, they have recently provided data communicationservices, or high speed data services. As mobile communication systemsevolve to provide more various services, they face lack of resources andusers' demands for high speed data services. Therefore, development ofmore advance mobile communication systems is required.

In order to conform to the requests, standardization of the 3^(rd)Generation Partnership Project Long Term Evolution (3GPP LTE) as thenext generation mobile communication system is ongoing. LTE is atechnology to implement high speed packet-based communication, up tomaximum 100 Mbps. To this end, various proposals have been discussed. Asan example, a scheme has been proposed to reduce the number of nodes oncommunication paths by simplifying network architecture. Another schemehas been proposed to apply wireless protocols to wireless channels.

FIG. 1 is a view of a general LTE mobile communication system.

Referring to FIG. 1, the wireless access network of the LTE mobilecommunication system includes an evolved Node B or an evolved UTRAN NodeB (EUTRAN), hereafter called eNB 110, a Mobility Management Entity (MME)120, a Serving Gateway (S-GW) 130, etc. User Equipment (UE) 100 isconnected to an external network through then eNB 110, the S-GW 130, anda Packet Data Network Gateway or Packet Data Network (PDN) Gateway,hereafter called P-GW 160.

eNB 110 is a Radio Access Network (RAN) node and corresponds to a RadioNetwork Controller (RNC) of a Universal Terrestrial Radio Access Network(UTRAN) system and a Base Station Controller (BSC) of a GSM EDGE RadioAccess Network (GERAN) system. eNB 110 is connected to UE 100 through awireless channel and performs functions similar to those of aconventional RNC/BSC. eNB 110 may simultaneously cover a number ofcells.

In LTE, since the user's traffic and real-time services, such as Voiceover IP (VoIP) service, are routed through shared channels, systems arerequired for collecting status information about UE devices 100 and forscheduling the UE devices. These systems are covered by the eNB 110.

MME 120 performs control functions. One MME 120 may be connected to anumber of eNBs.

S-GW 130 provides data bears. S-GW 130 creates or removes a bear underthe control of the MME 120.

Application Function (AF) 140 exchanges application-related informationwith a user in a level of application.

Policy Charging and Rules Function (PCRF) 150 controls policy related toa user's Quality of Service (QoS). Policy and Charging Control (PCC)rule corresponding to policy is transmitted to the P-GW 160. PolicyCharging and Rules Function (PCRF) 150 is an entity of controlling a QoSfor traffic and a charging service. In general, user plane (UP) refersto a path connecting UE 100 and an RAN node, i.e., eNB 110, S-GW 130,and P-GW 160, through which user's data is transmitted/received. Thepath between UE 100 and eNB 110 uses a wireless channel and is subjectedto the limitation of resources.

In a wireless communication system such as LTE, the unit of channel towhich QoS can be applied is an Evolved Packet System (EPS) bearer. OneEPS bear is used to transmit IP flows with the same QoS request. An EPSbear may be designated with a parameter related to QoS, including QoSClass Identifier (QCI) and Allocation and Retention Priority (ARP). TheQCI is a parameter defining the QoS priority as an integer. The ARP is aparameter to determine whether to accept or refuse the creation of a newEPS bear.

An EPS bear corresponds to a Packet Data Protocol (PDP) context of aGeneral Packet Radio Service (GPRS) system. One EPS bear belongs to PDN.The PDN has an Access Point Name (APN) as an attribute. If PDNconnection for an IMS service such as Voice over LTE (VoLTE) is formed,it must be created by using a well-known IMS APN.

In order to support voice calls, LTE networks employ an IMS-based VoLTEtechnology using a Packet Switched (PS) delivery or a circuit switchedfall back (CSFB) technology using a circuit switched (CS) delivery for a2G/3G system. In LTE networks, the term ‘VoLTE’ has the same concept as‘Voice over IMS (VoIMS).’

DISCLOSURE OF INVENTION Technical Problem

The present invention has been made in view of the above problems, andprovides a method that prevents, when a voice call is created andestablished between the calling party and the called party and voicedata start to be exchanged, part of the voice data from being lost andthus the quality of call service (QoS) from being degraded.

The present invention further provides a method that prevents the lossof any part of the called party's voice data to be transmitted to thecalling party in a state where: although, when the calling UE isdisconnected with the called UE within a time interval from a time pointthat the calling UE has sent a voice call setup request to the called UEand the called UE has received the request to a time point that thecalled party answers the call, it cannot receive the called party'svoice data from the called party's UE while the called party answers thecall and starts to speaks to the calling party, and makes are-connection with the calling UE.

Solution to Problem

In accordance with an exemplary embodiment of the present invention, thepresent invention provides a method of performing transmission/receptionof signals in an evolved Node B (eNB) of a mobile communication systemincluding: receiving a first message including service requestinformation from user equipment (UE); transmitting a second messageincluding the service request information to an Mobility ManagementEntity (MME); receiving a third message including context informationfor the UE from the MME; and determining an inactivity timer value forthe UE based on the context information.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides an evolved Node B (eNB) ofperforming transmission/reception of signals in a mobile communicationsystem including: a transceiver for performing transmission/reception ofsignals; and a controller for: controlling the transceiver; receiving afirst message including service request information from user equipment(UE); transmitting a second message including the service requestinformation to an Mobility Management Entity (MME); receiving a thirdmessage including context information for the UE from the MME; anddetermining an inactivity timer value for the UE based on the contextinformation.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides user equipment (UE) ofperforming transmission/reception of signals in a mobile communicationsystem including: a transceiver for performing transmission/reception ofsignals; and a controller for controlling the transceiver andtransmitting a first message including service request information to anevolved Node B (eNB). The eNB determines an inactivity timer value forthe UE based on context information that is determined according to theservice request information.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides a method of performingtransmission/reception of signals in an evolved Node B (eNB) of a mobilecommunication system including: receiving a message for a sending callfrom calling user equipment (UE); transmitting the message for a sendingcall to called UE; receiving a packet corresponding to the sending callfrom the calling UE or a server related to IP Multimedia Subsystem(IMS); and maintaining connection with the calling UE based on thereceived packet.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides an evolved Node B (eNB) ofperforming transmission/reception of signals in a mobile communicationsystem including: a transceiver for performing transmission/reception ofsignals; and a controller for: controlling the transceiver; receiving amessage for a sending call from calling user equipment (UE);transmitting the message for a sending call to called UE; receiving apacket for maintaining connection with the calling UE, in response tothe sending call, from the calling UE or a server related to IPMultimedia Subsystem (IMS); and maintaining connection with the callingUE based on the received packet.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides user equipment (UE) ofperforming transmission/reception of signals in a mobile communicationsystem including: a transceiver for performing transmission/reception ofsignals; and a controller for: controlling the transceiver; transmittinga message for a sending call to called UE to an evolved Node B (eNB);and transmitting a packet for maintaining connection with the UE, inresponse to the sending call, to the eNB.

In accordance with another exemplary embodiment of the presentinvention, the present invention provides an IP Multimedia Subsystem(IMS) related server of performing transmission/reception of signals ina mobile communication system including: a transceiver for performingtransmission/reception of signals; and a controller for: controlling thetransceiver; receiving a message for a sending call from calling userequipment (UE); transmitting the message for a sending call to calledUE; and transmitting a message for maintaining connection with thecalling UE to the calling UE.

Advantageous Effects of Invention

As described above, the embodiments can hold, when a voice call iscreated, the connection between the calling UE and the called UE untilthe call has been set up as the called party answers, thereby preventingthe loss of any part of the called′ party's voice data.

BRIEF DESCRIPTION OF DRAWINGS

The features and advantages of the invention will become more apparentfrom the following detailed description in conjunction with theaccompanying drawings, in which:

FIG. 1 is a view of a general LTE mobile communication system;

FIG. 2 is a signal flow chart that describes a state where incoming calland outgoing call are made according to an embodiment of the presentinvention;

FIG. 3 is a signal flow chart that describes a method where aninactivity timer is set to have a relatively large period of time whenan eNB uses an IMS-based voice service according to an embodiment of thepresent disclosure;

FIG. 4 is a signal flow chart that describes operation in acommunication system according to an embodiment of the presentdisclosure;

FIG. 5 is a signal flow chart that describes a method of transmittingtimer information during the handover according to an embodiment of thepresent disclosure;

FIG. 6 is a signal flow chart that describes a method of transmittingNAS messages, without interruption, by UE, to keep the connection, aftera VoIMS call setup request is made, according to an embodiment of thepresent disclosure;

FIG. 7 is a signal flow chart that describes a method of transmittingmessages, without interruption, by PGW, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure;

FIG. 8 is a signal flow chart that describes a method of transmittingmessages, without interruption, by UE, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure;

FIG. 9 is a signal flow chart that describes a method of transmittingmessages, without interruption, by CSCF, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure;

FIG. 10 is a signal flow chart that describes a method of continuouslytransmitting messages by an IMS or core network and discarding themessages by eNB in order to keep the connection when a VoIMS call setuprequest is created, according to an embodiment of the presentdisclosure; and

FIG. 11 is a signal flow chart that describes a method of continuouslytransmitting messages by UE in order to keep the connection when a VoIMScall setup request is created, according to an embodiment of the presentdisclosure.

MODE FOR THE INVENTION

Hereinafter, embodiments of the present invention are described indetail with reference to the accompanying drawings.

Detailed descriptions of well-known functions and structuresincorporated herein may be omitted to avoid obscuring the subject matterof the invention.

Part of the elements in the drawings is exaggerated in shape, omitted orschematically shown to focus on the invention. In the drawings, the sameor similar elements are denoted by the same reference numbers.

The features and advantages of the invention and the methods toaccomplish the objectives of the invention will become more apparentfrom the following detailed description and the accompanying drawings.Although embodiments of the invention have been described in detail, itshould be understood that many variations and modifications of the basicinventive concept herein described, which may be apparent to thoseskilled in the art, will still fall within the spirit and scope of theexemplary embodiments of the invention as defined in the appendedclaims.

In addition, it should be understood that the blocks in the signalflowcharts and the combinations in the flowcharts can be performed viacomputer programming instructions. These computer programminginstructions can be installed to processors of data processing equipmentthat can be programmed, special computers, or universal computers. Theinstructions, performed via the processors of data processing equipmentor the computers, can create means that perform functions described inblocks of the flow charts. In order to implement functions in aparticular mode, the computer programming instructions can be stored ina computer available memory or computer readable memory that can supportcomputers or data processing equipment that can be programmed.Therefore, the instructions, stored in the computer available memory orcomputer readable memory, can be installed to the products, and performthe functions described in the block(s) of the flow charts. In addition,since the computer programming instructions can also be installed tocomputers or data processing equipment that can be programmed, they cancreate computer-executable processes as a series of operations areperformed therein, described in the block(s) of the flow charts therein.

The blocks of the flow charts refer to part of codes, segments ormodules that include one or more executable instructions to perform oneor more logic functions. It should be noted that the functions describedin the blocks of the flow charts may be performed in a different orderfrom the embodiments. For example, the functions described in twoadjacent blocks may be performed at the same time or in reverse order.

In the embodiments, the terminology, component ‘-unit,’ refers to asoftware element or a hardware element such as a PGGA, an ASIC, etc.,and performs a corresponding function. It should be, however, understoodthat the component ‘-unit’ is not limited to a software or hardwareelement. The component ‘-unit’ may be implemented in storage media thatcan be designated by addresses. The component ‘-unit’ may also beconfigured to regenerate one or more processors. For example, thecomponent ‘-unit’ may include various types of elements (e.g., softwareelements, object-oriented software elements, class elements, taskelements, etc.), segments (e.g., processes, functions, achieves,attribute, procedures, sub-routines, program codes, etc.), drivers,firmware, micro-codes, circuit, data, data base, data structures,tables, arrays, variables, etc. Functions provided by elements and thecomponents ‘-units’ may be formed by combining the small number ofelements and components ‘-units’ or may be divided into additionalelements and components ‘-units.’ In addition, elements and components‘-units’ may also be implemented to regenerate one or more CPUs indevices or security multi-cards.

Hereinafter, exemplary embodiments of the present invention aredescribed in detail with reference to the accompanying drawings. Thesame reference numbers are used throughout the drawings to refer to thesame or similar parts. Detailed descriptions of well-known functions andstructures incorporated herein may be omitted to avoid obscuring thesubject matter of the invention.

Although embodiments of the present disclosure will be described basedon OFDM-based wireless communication systems, or the 3GPP EUTRAstandard, and a VoLTE service, it will be appreciated to those skilledin the art that the subject matter of the present invention can beapplied to other communication systems and services with a similartechnical background and channel format without departing from the scopeof the present invention. It should be understood that the VoLTE-basedtechnology described in the present disclosure may be applied to otherIMS-based voice services (e.g., Voice over WiFi). It should beunderstood that the messages and packets are interchangeably used in thepresent disclosure.

It should be understood that each of the communication entities in thepresent disclosure includes a transceiver for transmitting/receivingsignals to/from the other communication entities and a controller forcontrolling the transceiver and the operations of the communicationentities based on data transmitted/received through the transceiver.

Although embodiments of the present invention will be described based onstates where, after transmitting an invite message, a calling userequipment (UE) receives 100 trying message or 180 ringing message ordoes not explicitly receive the messages, or a combination of thestates, since transmitting/receiving the 100 trying message or 180ringing message is optional, the subject matter of the present inventionmay be identically applied to the other modifications, etc., regardlessof transmission/reception of the 100 trying message or 180 ringingmessage. In the following embodiments, 100 trying message, 180 ringingmessage, 603 decline message, and 200 OK message are used for a casewhere a Session Initiation Protocol (SIP) message includes a responsecode representing 100 trying message, 180 ringing message, 603 declinemessage or 200 OK message.

Although embodiments of the present disclosure will be described basedon a case where the eNB and user equipment (UE) are disconnected when atransmission/reception packet for the UE is not created in the eNB untilan inactivity time period of an inactivity timer has expired from theinitial value set by the eNB, it should be understood that the subjectmatter of the present invention may also be applied to a case where theeNB and user equipment (UE) are disconnected when atransmission/reception packet for the UE is not created in the eNBwithin the inactivity time period.

First, a case where a problem occurs in an LTE mobile communicationsystem is described. FIG. 2 is a signal flow chart that describes astate where incoming call and outgoing calls are made according to anembodiment of the present invention.

Referring to FIG. 2, the communication system performstransmission/reception of signals among calling UE 201, calling partyeNB 202, calling party CSCFs 203, called UE 204, called party eNB 205and called party CSCFs 206. The embodiment includes a case where part ofuser's voice data is not transmitted in the communication system, or acall is dropped.

The calling UE 201 transmits an invite message for making a call to thecalled UE 204 (210).

After receiving the invite message, the called UE 204 transmits a 100trying message to the calling UE 201 (215), and also transmits a 180ringing message informing that the phone is ringing to the calling UE201 (220).

The calling UE 201 receives the 100 trying message and the 180 ringingmessage including the called UE's states (225 and 230).

When the called UE 204 answers, or does not decline, the callimmediately after the phone starts ringing, the calling UE 201 may havea relatively long period of time without transmitting/receiving anypacket to/from the network.

When the eNB 202 detects that the state continues (i.e., where thetransmitting/receiving of data or signals is not performed) for a presetperiod of time set to a timer (235), it releases connection (or RRC)from the calling UE 201 (240).

At this state, when the called user of the called UE 204 accepts thecall (245), the called UE 204 transmits a 200 OK message for informingthat the called user's call acceptance to the calling UE 201 (250), andthe called user simultaneously starts to speak to the calling user sincehe/she has already accepted to the call (255). At this state, since thecalling UE 201 has released the RRC, the network (CSCFs) 203 performs apaging process to establish connection with the calling UE 201 (260) andthe calling UE 201 thus performs a service request procedure (265). Theservice request procedure includes an RRC connection setup.

Since paging transmission/reception and connection establishment take aperiod of time, the voice data corresponding to a speech that the calledusers has made to the calling user during the period of time may belost, i.e., voice media drop (275).

In order to resolve the problem, the present invention is implemented,showing a variety of embodiments. That is, they provide systems to holdthe connection between the calling UE and called UE from when thecalling UE transmits an invite message to make a call to the called UEuntil it receives a 200 OK message from the called UE (270).

When the eNB detects that any packet (signaling and data) to betransmitted/received to/from UE has not been created for over a periodof time, it releases connection (RRC and/or S1 connection) from the UE.For this process, a timer is used and it is generally called to aninactivity timer.

In order to prevent the release of connection between the calling UE andthe called UE: the inactivity timer needs to set the initial value to arelatively large value to keep the connection from when the calling UEtransmits an invite message to the called UE until the calling UEreceives the 200 OK message from the called UE; or signals or packetsfor UE need to be created and transmitted to eNB.

FIG. 3 is a signal flow chart that describes a method where aninactivity timer is set to have a relatively large period of time whenan eNB uses an IMS-based voice service according to an embodiment of thepresent disclosure.

Referring to FIG. 3, UE 302, eNB 304 and MME 306 are communicating witheach other.

UE 302 transmits an RRC setup request message including a servicerequest to eNB 304 in order to establish connection with eNB 304 (310).The service request is transmitted to MME 306.

After receiving the RRC setup request message, eNB 304 transmits theservice request to the MME 306 (315).

MME 306 transmits an Initial UE context setup message including contextfor UE 302 to the eNB 304, in response to the received message (320).For example, the context for UE 302 may include information about abearer that the UE 302 is using.

The eNB 325 adjusts the inactivity timer value based on the bearercontext transmitted from the MME 306 (325). For example, when the eNB325 detects that UE 302 is in a state where it performs an IMS signalingwith the network, it may apply a larger value of inactivity timer to thecurrent state than the previous state. When the bearer context of UE 302includes a bearer of QCI 5, eNB detects that UE 302 uses VoIMS. Sincethe problem described above may occur because of the latent release ofthe connection, the inactivity timer may set the initial value to avalue (e.g., 30 or 60 seconds) larger than the default value (e.g., 10seconds). That is, the eNB 304 sets a larger inactivity timer to UE witha QCI 5 bearer than other UE, thereby keeping the connection for the UE,without disconnection, although any transmission/reception packet is notcreated for a relatively long period of time.

The method of applying a relatively large inactivity timer to UE usingVoIMS is implemented as follows.

As a first example, in a state where a configuration for a number ofinactivity timer initial values has been preset, one of the values isselected as a default configuration and applied to UE. When the UEsatisfies the condition (i.e., a condition of using VoIMS), aconfiguration with a value larger than the initial value of the timerset according to the default configuration is selected and applied tothe UE. For example, in a state where a default configuration has beenset in such a way that the initial value of the inactivity timer is 10seconds and an additional configuration is set in such a way that theinitial value of the inactivity timer is 30 seconds, when UE satisfiesthe same condition as eNB uses VoIMS, the additional configuration isselected and applied to the UE. In other embodiments, the configurationvalue may be determined according to a preset value (preset values) orbased on the signaling with respect to the network.

As a second example, in a state where a default configuration is appliedto UE, when the UE satisfies the condition (i.e., a condition of usingVoIMS), an additional value is added to the initial value of theinactivity timer included in the default configuration and the result isapplied to the inactivity timer. For example, in a state where theinitial value is 10 seconds and an additional value is 20 seconds, whenUE satisfies the conditions, eNB adds the additional value 20 second tothe initial value 10 and uses 30 seconds as the initial value of theinactivity timer. In other embodiments, the initial value and/or theadditional value may be determined according to a preset value (presetvalues) or based on the signaling with respect to the network.

As a third example, in a state where an inactivity timer as a defaultconfiguration is applied to UE once, when the UE satisfies the condition(i.e., a condition of using VoIMS), the inactivity timer is applied tothe UE twice or more times. For example, in a state eNB has been setwith a default configuration where the initial value of the inactivitytimer is 10 seconds and the application frequency is one, when UE usingVoIMS satisfies the conditions, the inactivity timer is applied to theUE three times. This is a similar effect as the inactivity timer for UEusing VoIMS increases to 30 seconds. In other embodiments, theapplication frequency of timers may be determined according to a presetvalue (preset values) or based on the signals transmitted to/from thenetwork.

FIG. 4 is a signal flow chart that describes operation in acommunication system according to an embodiment of the presentdisclosure. When eNB requests an IMS-based voice service, the inactivitytimer may be set to a relatively large period of time for a specificstate.

Referring to FIG. 4, UE 402, eNB 404, MME 406 and SGW 406 arecommunicating with each other.

UE 402 transmits an RRC setup request message to eNB 404 in order toestablish connection with eNB 404 (410). The RRC setup request messageincludes a service request message. The service request is transmittedto MME 406.

After receiving the RRC setup request message, eNB 404 transmits anInitial UE message including the service request to the MME 406 (415).

MME 406 transmits an Initial UE context setup message including contextfor UE 402, i.e., context of bearers that the UE 402 is using, to theeNB 404, in response to the received message (420).

The eNB 404 ascertains that the UE 402 is in a state where it mayperform an IMS signaling with the network, based on the bearer contexttransmitted from the MME 406. When the bearer context of UE 402 includesa bearer of QCI 5, the eNB detects that UE 402 uses VoIMS.

The eNB 404 transmits an RRC setup message for establishing RRC to theUE 402 (425).

After establishing RRC with UE 402, when the eNB ascertain that UE 402is in a state where it may perform an IMS signaling with the network(430), e.g., when packers are transmitted through a bearer of QCI 5 (alogical channel with respect to the eNB), the eNB 404 detects that theUE 402 is performing transmission of packets related to a real VoIMSservice.

During the process, when the eNB 404 releases the connection with the UE402 earlier, the problem described above may occur. To prevent theoccurrence of the problem, the eNB 404 sets the initial value of theinactivity timer to a value (e.g., 30 or 60 seconds) larger than thedefault value (e.g., 10 seconds) in operation 430. That is, the eNB 404keeps the connection with UE performing an IMS signaling, i.e., UE 402that transmits packets through a bearer of QCI 5, for a larger period oftime than with the other UE, although any transmission/reception packetis not created. Unlike the embodiment shown in FIG. 3, the embodiment ofFIG. 4 is designed in such a way that the eNB 404 sets the initial valueof the inactivity timer to a relatively large value only for the UE 402that transmits VoIMS related packets through a bearer of QCI 5, therebypreventing the resources of the eNB 404 from being wasted and reducingthe battery power consumption of the UE 402.

The method of applying a relatively large inactivity timer to UE usingVoIMS is implemented as follows.

As a first example, in a state where a configuration for a number ofinactivity timer initial values has been preset, one of the values isselected as a default configuration and applied to UE. When the UEsatisfies the condition (i.e., a condition of using VoIMS), aconfiguration with a value larger than the initial value of the timerset according to the default configuration is selected and applied tothe UE. For example, in a state where a default configuration has beenset in such a way that the initial value of the inactivity timer is 10seconds and an additional configuration is set in such a way that theinitial value of the inactivity timer is 30 seconds, when UE satisfiesthe same condition as eNB uses VoIMS, the additional configuration isselected and applied to the UE. In other embodiments, the configurationvalue may be determined according to a preset value (preset values) orbased on the signaling with respect to the network.

As a second example, in a state where a default configuration is appliedto UE, when the UE satisfies the condition (i.e., a condition of usingVoIMS), an additional value is added to the initial value of theinactivity timer included in the default configuration and the result isapplied to the inactivity timer. For example, in a state where theinitial value is 10 seconds and an additional value is 20 seconds, whenUE satisfies the conditions, eNB adds the additional value 20 second tothe initial value 10 and uses 30 seconds as the initial value of theinactivity timer. In other embodiments, the initial value and/or theadditional value may be determined according to a preset value (presetvalues) or based on the signaling with respect to the network.

As a third example, in a state where an inactivity timer as a defaultconfiguration is applied to UE once, when the UE satisfies the condition(i.e., a condition of using VoIMS), the inactivity timer is applied tothe UE twice or more times. For example, in a state eNB has been setwith a default configuration where the initial value of the inactivitytimer is 10 seconds and the application frequency is one, when UE usingVoIMS satisfies the conditions, the inactivity timer is applied to theUE three times. This is a similar effect as the inactivity timer for UEusing VoIMS increases to 30 seconds. In other embodiments, theapplication frequency of timers may be determined according to a presetvalue (preset values) or based on the signals transmitted to/from thenetwork.

The eNB 404 transmits the received packet to the SGW 408 (435).

The two embodiments described above are implemented in such a way that:when UE uses a bearer of QCI 5 or transmits real packets through abearer of QCI 5, eNB sets the initial value of the inactivity timer to arelatively large value. In another embodiment, MME determines theinitial value of the inactivity timer and transmits it to eNB. MMEdetermines whether UE performs an IMS signaling with the network. Thatis, MME determines whether UE uses a VoIMS service, based on QCI or APNof a PDN for the UE. For example, MME determines whether UE receives aVoIMS service, based on one or more of the following cases or thecombination thereof: a case where UE has a PDN connection with IMS asAPN, a case where UE has an EPS bearer of QCI 5 and a case where UEsubscription information is set in such a way that UE uses VoIMS. WhenMME ascertains that UE has been using VoIMS, it requests eNB to apply alarger initial value of the inactivity timer to the UE than to UE thatdoesn't use VoIMS. To this end, MME may an Initial Context Setup Requestmessage including initial inactivity timer IE to eNB. The initialinactivity timer IE includes an initial value of the inactivity timerthat eNB will use. When eNB receives an Initial Context Setup Requestmessage without an initial inactivity timer IE, it may apply a defaultvalue to the initial value of the inactivity timer. The embodiment maybe implemented in such a way that the Initial Context Setup Requestmessage includes an initial inactivity timer IE greater than a defaultvalue for UE that uses VoIMS and does not an initial inactivity timer IEfor UE that does not use VoIMS.

Although the embodiments are implemented in such a way that adetermination is made as to whether UE uses VoIMS based on bearercontext (QCI, APN, etc.), they may be modified in such a way that thedetermination as to whether UE uses VoIMS is made based on packetinspection.

For example, when a network node receives a packet from UE over aservice provider network, it applies Deep Packet Inspection (DPI) to thereceived packet and determines whether the received packet includes anINVITE message for starting call configuration. To do this, the networknode detects whether the content of the packet from the UE starts withinformation representing an SIP INVITE message, e.g., “INVITE sip:” inthe leading part of the packet. The detection function may beimplemented in the eNB or any one node except for the eNB. When the nodewith the detection function is separated from the eNB, the detectionresult, i.e., the determination as to whether the received packet is acall configuration message, INVITE, is transmitted to the eNB.

In order to control load for the detection process, the detection forthe call configuration request message is applied to not all of thepackets but to only VoIMS related packets, e.g., a packet transmittedthrough a bearer with QCI 5 or a packet transmitted through a PDNconnection with an APN of IMS.

FIG. 5 is a signal flow chart that describes a method of transmittingtimer information during the handover according to an embodiment of thepresent disclosure. More specifically, FIG. 5 shows a diagramillustrating a method of transmitting, when S1 handover occurs, theinformation from a first eNB through MME to a second eNB.

Referring to FIG. 5, transmission/reception of signals may be performedamong a source eNB 502, MME 504, and a target eNB 506.

When UE that transmits/receives signals to/from the source eNB 502undergoes a handover from a source network to a target network in themiddle of setting a VoIMS call, the information indicating that arelatively larger inactivity timer needs to be used, described in theforegoing embodiments, is required to be transmitted a second network(the target network).

When a handover is needed for UE, the source network may transmitinformation to the MME 504, including an identifier, indicating that arelatively larger inactivity timer needs to be applied to the UE, and/orthe initial value of the inactivity timer (510).

MME 504 transmits a handover request message including the informationreceived in operation 510 to the second network including the target eNB506 (515). After receiving the handover request message, the secondnetwork applies a relatively larger inactivity timer based on theidentifier or applies the initial value of the inactivity timertransmitted from the first network. When the type of handover is an X2handover, the identifier or the initial value of the inactivity timermay be included in an X2 Handover Request message and then transmitted.When the type of handover is an S1 handover, the identifier or theinitial value of the inactivity timer may be included in an S1 HandoverRequest message and then transmitted to MME. After that, the S1 HandoverRequest message may be transmitted to the second network through theMME. When S1 handover is used, the identifier or the initial value ofthe timer is included in a field of a transparent container inserted tothe S1 message and then transmitted.

The embodiments of the present disclosure described above were relatedto methods that keep the connection for UE using a voice service as longas possible. The following embodiments of the present disclosure includemethods of continuously transmitting/receiving packets so that eNB maykeep the connection.

According on embodiment of the present disclosure, after UE makes aVoIMS outgoing request (transmits an Invite message), the UE transmitsNAS messages to the MME until the UE receives the final response (a 200OK message) so that the connection can be kept.

Since the NAS message that UE transmits to the MME is transmittedthrough eNB, when the transmission is detected, the eNB disconnects theUE. At the moment, the NAS message transmitted by UE may include an EMMstatus message, and cause of the EMM status message may include an EMMcause that allows the MME that has received an EMM status message fromthe UE to ignore an EMM status message that is received without anyother operation or without altering the status for the UE.

For example, EMM cause of an EMM status message may be “dummy”indicating a meaningless EMM status message, “connection alive”indicating the connection retention, “ignore required” indicatingreception and ignorance by MME, etc. As such, MME receives the indicatedNAS messages and ignores the corresponding EMM status messages.

FIG. 6 is a signal flow chart that describes a method of transmittingNAS messages, without interruption, by UE, to keep the connection, aftera VoIMS call setup request is made, according to an embodiment of thepresent disclosure.

Referring to FIG. 6, signals may be transmitted/received betweenentities of the communication system including calling UE 601, eNB 602,MME 603, PGW 604 and called UE 605. Communication entities that are notdirectly related to the embodiment will be omitted in the description.

The calling UE 601 transmits an invite message for configuring a voicecall to the called UE 605 (610).

When the called UE 605 transmits a 100 trying message or a 180 ringingmessage, the calling UE 601 may receive the messages (615).

The calling UE 601 may repeatedly create and transmit a message to theeNB 602 to keep the connection state until the called UE 605 accepts acall in at least one interval of the following: after the calling UE 601transmits the invite message and after the calling UE 601 receives the180 ringing message, and at least one of the following cases issatisfied, which are: before the call has been configured and before thecalled UE 605 declines the call (620 and 630). At this moment, in theembodiment, the message may include an NAS message. Since the NASmessage is transmitted, in a form of RRC message, more specifically, aform of message included in an ULInformationTransfer message, to the MME603 through the eNB 602, the eNB 602 detects that packettransmission/reception for UE 601 has occurred and may not perform theconnection releasing (635).

As described above, the NAS message created and transmitted by UE 601may be an EMM status message including a cause indicating that EMM 603has received the message and then may not need to perform an additionaloperation or to alter the status. The NAS message may be an Uplink NAStransport or Uplink Generic NAS transport including a cause indicatingthat UE 601 similarly transmits a dummy message or MME 603 receives amessage and may ignore the message. In that case, the message containerincluded in the message may not include any information. MME 603 mayignore the received message (640). According to embodiments, UE 601 maytransmit the NAS message, every a period of time, until at least one ofthe following cases is satisfied, which are: before a call has been setup and a voice call starts and a case where the called UE 605 declinesthe call setup. The period of time may be less than the initial value ofthe general inactivity timer of eNBs (e.g., 8 seconds).

The UE 601 may use at least one of the following: an event to receive a200 OK message transmitted from the called UE 605 and an event todecline a call setup request transmitted from the called UE 605, e.g.,an event to receive a 603 decline message, as a standard for determininga point of time when transmission of the NAS is stopped (645 and 650).

In another embodiment of the present disclosure, in order to keep theconnection with UE, PGW may continue creating messages and transmittingthe messages to the UE. More specifically, in a state where UE is usingVoIMS, when PGW installs a packet filter in the UE so that the UE candiscard packets transmitted from a specific address (or a combination ofports) and the calling UE requests a VoIMS setup, the PGW periodicallycreates a packet transmitted from an address that may match with theinstalled filter and transmits the created packet to the UE. In theembodiments, the packet may be a dummy packet. In description of theembodiments of the present invention, the payload of the dummy packetdoes not include any information or includes information that does notrequire a specific operation in the called party or transmission node ordoes not cause the state alteration.

The packet transmission may cause the eNB not to perform the connectionrelease and UE may directly discard packets received by the installedpacket filter.

FIG. 7 is a signal flow chart that describes a method of transmittingmessages, without interruption, by PGW, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure.

Referring to FIG. 7, signals may be transmitted/received between UE 702,eNB 704, MME 706, and PGW 708.

When a PDN connection or EPS bearer is formed for UE 702 (710), the PGW708 creates a packet filter with a specific address (or a combination ofports) and may transmit the packet filter to the UE 702 through the MME706 (715). The packet filter may include, when the UE 702 receives amatching packet, information about the content where a discardingoperation needs to be performed. In the embodiment, the packet filterperforming the function may be called a discard packet filter.

The UE 702 configures the received packet filter and may perform afunction corresponding to the packet filter (720).

As an example, PGW 708 sets: the address of the packet filter to apreset address (e.g., 0.0.0.0.); the direction to downlink; and thereport port to 9 (discard port), and may set UE 702 so that packetsreceived through the address are all discarded. The packet filter may beincluded, as a TFT, in a message, Create Session response/Create BearerRequest, transmitted to the SGW. The SWG receives the packet filter andtransmits the received packet filter to the MME 706.

MME 706 includes the received packet filter (TFT) information in Activedefault/dedicated EPS bearer context request transmitted to UE.

In the embodiment, the creation and transmission of the packet filter bythe PGW 708 may be performed, only when the UE 702 creates EPS bearer ofPDN connection related to VoIMS, or according to information SDFtemplate of a PCC rule transmitted from PCRF.

In addition, the creation and transmission of the packet filter to theUE 702 may be performed at a point of time when a bearer is formed andwhen the bearer context is altered. In that case, an update/modifybearer request message instead of Create Session response/Create BearerRequest and a modify EPS bearer context request message instead ofActive default/dedicated EPS bearer context request may be used.

When a VoIMS call is created, the UE 702 transmits an invite message tothe PGW 708 (725). When the PGW 708 receives the invite message andrecognizes that a call setup starts, it periodically creates andtransmits messages in order to keep the connection with the calling UE702.

The recognition (735) of a call setup by the PGW 708 may include atleast one of the following cases: where the PGW 708 analyzes a packettransmitted from the calling UE 702 and ascertains that the analyzedpacket is an invite message; and where the PGW 708 analyzes a packettransmitted from the called party and ascertains that the analyzedpacket is a 180 ringing message or 100 trying message (730).

The PGW 708 may periodically transmit a dummy packet after a call hasbeen set up and until the call starts or before the call is declined(740). In the embodiment, the period for transmitting the dummy packetmay be less than the initial value of the general inactivity timer ofeNBs 704 (e.g., 8 seconds). The PGW 708 may non-periodically transmit adummy packet to the UE 702 at an arbitrary time. The eNB 704transmitting the dummy packet as describe above may keep the connectionwith the UE 702 in order to perform transmission of the dummy packet(745).

The UE 702 may discard the received dummy packet, based on the packetfilter that has been set up through operation 720 (750).

As an example, after 8 second has elapsed from a point in time when thePGW 708 received a 180 ringing message, the PGW 708 may create andtransmit dummy packets every 8 seconds. The PGW 708 may use at least oneof the following: an event to receive a 200 OK message transmitted fromthe called party (755) and an event to receive a call decline message,e.g., an event to receive a 603 decline message, as a standard fordetermining a point in time when transmission of the message is stopped.

In the embodiment, the transmission address of the dummy packet createdby the PGW 708 may use an address corresponding to the address includedin the packet filter that has been transmitted to the UE 702.

When the dummy packet is transmitted to UE 702 through eNB 704, the UE702 discards packets that are received through the packet filter set inoperation 720. Meanwhile, PGW 708 may not create charge information forthe dummy packets.

In another embodiment of the present disclosure, in order to keep theconnection with UE, the UE may continuously create messages and transmitthe messages to PGW. More specifically, UE may transmit an uplink packetfilter to PGW so that packets transmitted from a specific address (or acombination of ports) can be discarded. In the embodiment, the UE may beUE at the calling party (calling UE).

After the calling UE transmits an invite message or when the calling UEreceives a 180 ringing message and/or a 100 trying message from thecalled party, the UE periodically creates a packet corresponding to anaddress that may match with the installed uplink packet filter andtransmits the packet to PGW. In the embodiment, the packet that maymatch with the uplink packet filter and is ignored or discarded by PGWis called a dummy packet. The packet transmission may cause the eNB notto perform the connection release, and PGW may directly discard packetsreceived by the installed packet filter.

FIG. 8 is a signal flow chart that describes a method of transmittingmessages, without interruption, by UE, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure.

Referring to FIG. 8, at least one of the following entities: calling UE802, eNB 804, MME 806, and PGW 808 may transmit/receive signals to/fromthe other entities.

In the embodiment, when a PDN connection or EPS bearer is formed for theUE 802 (810), the UE 802 creates a packet filter with a specific address(or a combination of ports) and may transmit the packet filter to thePGW 808 through the MME 806 and SGW (815).

The packet filter may include, when the PGW receives a matching packet,information for performing a discarding operation. For example, UE sets:the address of the packet filter to a preset address (e.g., 0.0.0.0.);the direction to uplink; and the report port to 9 (discard port), andmay request the PGW 808 so that packets received through the address areall discarded. The packet filter may be included, as a TAD, in amessage, bearer resource modification/addition request, transmitted tothe MME 806. The MME 806 receives the packet filter and transmits thereceived packet filter to the PGW 808 through SGW (820). In theembodiment, the modify bearer command transmitted from the MME 806 tothe SGW includes the same packet filter (TDA), and the SGW receives thepacket filter and may transmit the same information to the PGW 808.Meanwhile, UE may obtain an address that will be used for the packetfilter (e.g., IP address and port number) through Protocol ConfigurationOption (PCO) transmitted from the PGW. That is, when PDN connection orEPS bearer is formed, the PGW includes an address to be used for thepacket filter in the PCO and transmits a message, create sessionresponse (when PDN connection is formed)/Create bearer request (when EPSbearer is formed) with the address. At the moment, the PCO may include acontainer ID indicating that UE needs to use a discard packet filter inthe uplink direction as well as the address (e.g., IP address and portnumber). When the PCO is transmitted to MME through S-GW, the MMEincludes the PCO in an ESM NAS message (e.g., activate/modify EPS bearercontext request) to be transmitted to UE and transmits the message tothe UE. As described above, UE receives the PCO, and may determine thata discard packet filter for a specific address is required, based oninformation included in the PCO. Therefore, UE may create a discardpacket filter creating request and transmit the request.

The PGW 808 may have or set a packet filter that may discard or ignorean uplink packet transmitted through a specific address (820). In theembodiment, when UE 802 has PDN connection or EPS bearer related toVoIMS, the UE 802 may also be applied to a method of creating andtransmitting the packet filter.

When a VoIMS call is created, the UE 802 may transmit an invite messageto called UE (825).

The UE 802 may receive at least one of the following: a 180 ringingmessage and a 100 trying message from the called UE (830).

The PGW 808 may detect the Invite message (835). The process ofdetecting the Invite message may be performed after at least one ofoperations 825 and 830.

When calling UE 802 recognizes that a call setup starts, the calling UE802 may periodically create a packet corresponding to the packet filterand transmit the packet filter in order to keep the connection (840). Inthe embodiment, the packet that corresponds to the packet filter and is,if received by PGW 808, ignored or discarded by the PGW 808 may becalled a dummy packet.

The eNB 802 that receives or transmits a message including the dummypacket may keep the connection with the UE 802 (845).

The PGW 808 may discard or ignore the dummy packet according to the setpacket filter (850).

In the embodiment, the creation and transmission of the dummy packet bythe calling UE 802 may start: after the calling UE 802 transmits aninvite message or when the calling UE 802 analyzes a packet transmittedfrom the called UE and ascertains that the analyze packet is at leastone of the following: a 180 ringing message and a 100 trying message.The UE 802 may periodically transmit the dummy packet, every a period oftime, after a call has been set up and until the call starts. The periodof time may be less than the initial value of the general inactivitytimer of eNBs (e.g., 8 seconds).

For example, after 8 seconds have elapsed from a point in time when theUE 802 received a 180 ringing message, the UE 802 may periodicallycreate and transmit messages every 8 seconds. The UE 802 may use atleast one of the following: an event to receive a 200 OK messagetransmitted from the called party and an event to receive a call declinemessage, e.g., an event to receive a signal including a 603 Declinemessage, as a standard for determining a point in time when transmissionof the message is stopped (855).

After receiving at least one of the 200 OK message and the call declinemessage, the calling UE 802 may stop transmitting the dummy packet(860).

The address for the dummy packet created by the UE 802 needs to use anaddress corresponding to the address included in the packet filterdescribed above. When the message is transmitted to the PGW 808, the PGW808 discards or ignores a packet received by the packet filter set inthe previous process. Meanwhile, in the embodiment, the PGW 808 may notcreate charge information for the message.

In another embodiment of the present disclosure, in order to keep theconnection with UE, an entity of an IMS network (e.g., CSCF) maycontinuously create messages and transmit the messages to UE. Morespecifically, when UE requests an outgoing call, the CSCF at the callingparty periodically creates a message and transmits the message to thecalling UE until the call has been set up. Since the message istransmitted to the UE through eNB, the connection with the UE may bekept. The message created by the CSCF may include a message that doesnot affect a call processing unit of the UE, e.g., a 180 ringingmessage.

FIG. 9 is a signal flow chart that describes a method of transmittingmessages, without interruption, by CSCF, to keep the connection, when aVoIMS call setup request is created, according to an embodiment of thepresent disclosure.

Referring to FIG. 9, calling UE 901, eNB 902, PGW 903, CSCF 904 andcalled UE 905 may transmit/receive signals to/from the other entities inthe communication system.

When a VoIMS call is created, the calling UE 901 may transmit an invitemessage to the called UE 905 (910).

When the CSCF 904 recognizes that a call setup starts (915), it mayperiodically create a message to keep the connection with the calling UE901 (920) and may transmit the created message to the calling UE 901(925).

The recognition of a call setup by the CSCF 904 may be implemented with:a process where the CSCF 904 analyzes a packet transmitted from thecalling UE 901 and ascertains that the analyzed packet is an invitemessage; or a process where the CSCF 904 analyzes a packet transmittedfrom the called UE 905 and ascertains that the analyzed packet is a 180ringing message or 100 trying message.

The CSCF 904 may periodically transmit the message to the calling UE901, every a period of time, after a call has been set up and until thecall starts. The period of time may be less than the initial value ofthe general inactivity timer of eNBs 902 (e.g., 8 seconds).

For example, after 8 seconds have elapsed from a point in time when theCSCF 904 received a 180 ringing message, the CSCF 904 may periodicallycreate and transmit messages every 8 seconds.

The CSCF 904 may use reception of at least one of the following: a 200OK message and a call decline message, as a standard for determining apoint in time when transmission of the message is stopped (940).

In the embodiment, the message created and transmitted by the CSCF 904may include at least one of the status information providing messagessuch as a 180 ringing message and a 183 session in progress, so that theconnection can be kept without affecting the operation of a callprocessing unit of the calling UE 901. In the embodiment, when thecalling UE 901 receives a 180 ringing message or a 183 session inprogress in multiple manner, it may ignore the received message so asnot to affect a call processing.

Meanwhile, in another embodiment of the present disclosure, a method isproposed where a message created and transmitted by CSCF or PGW can bediscarded by eNB before the message is transmitted to UE in order tokeep the connection with the UE. The eNB is set with a policy so that,when the eNB receives a downlink packet with a GTP-U header including aspecific marking, transmitted from S-GW, the eNB keeps the connectionwith the UE and discards the packet. Like the embodiments describedabove, when a VoIMS call setup is created from a calling UE, CSCF or PGWstarts to create and transmit a 180 ringing message (by CSCF) or aspecific packet (by PGW) in order to keep the connection state of theUE. When PGW transmits the packets to SGW, the PGW may include thespecific marking information, described above, in the GTP-U. The packetwith the GTP-U header including the same marking information istransmitted to the eNB through the S-GW. The eNB keeps the connectionwith the UE and discards the received packet without transmitting thepacket to the UE, according to the set policy.

FIG. 10 is a signal flow chart that describes a method of continuouslytransmitting messages by an IMS or core network and discarding themessages by eNB in order to keep the connection when a VoIMS call setuprequest is created, according to an embodiment of the presentdisclosure.

Referring to FIG. 10, the communication system according to theembodiment performs transmission/reception of signals among UE 1001, eNB1002, MME 1003, gateway (GW) 1004 and PCRF 1005. The GW 1004 of theembodiment may include at least one of the PGW and SGW.

The eNB 1002 may be set with a policy (including FQI controlinformation) (1015) so that, when the eNB 1002 receives a packet with aGTP-U header including specific marking information (1010), the eNB 1002keeps the connection with UE that will receive the packet and discardsthe packet without transmitting the packet. The policy may be setthrough a Q&M method or may be created by a specific policy server(e.g., PCRF 1005) and then transmitted to the eNB 1002 through a corenetwork node.

As the embodiment described above, when the UE 1001 requests a VoIMScall by an Invite message (1020), the entity (CSCF) of the IMS networkor the entity (PGW) 1004 of the core network detects the Invite message(1025). The entity 1004 of the core network may periodically create amessage and transmit the message to the calling UE 1001 in order to keepthe connection with the calling UE 1001 (1030).

At the moment, if PGW 1004 analyzes packets created and transmitted byCSCF and recognizes a packet to keep the connection state from theanalyzed packets or directly creates a packet to keep the connectionstate, the PGW 1004 includes specific marking information in the GTP-Uheader of the packet when the packet is transmitted to S-GW. The markinginformation needs to be set corresponding to the marking informationapplied to the policy set by the eNB 1002.

In the embodiment, when S-GW receives a packet including the markinginformation, the same marking information may be included in the headerof the GTP-U message to be transmitted to the eNB 1002.

When the eNB 1002 receives a packet including the marking information inthe GTP-U header, the eNB 1002 determines that activity for adestination UE 1001 exists (i.e., to maintain the connection state);however, the eNB 1002 may discard the real message without transmittingthe real message to the UE 1001 (1035).

The PGW 1004 may receive at least one of the following: a 200 OK messageand a call decline message such as a 603 Decline message from the calledUE (1040).

The PGW 1004 may stop transmitting a packet with specific markinginformation to the eNB 1002, based on the received message (1045).

The PGW 1004 may transmit at least one of the received 200 OK messageand the call decline message to the UE 1001 (1050).

In another embodiment of the present disclosure, when calling UEtransmits an outgoing call to called UE, in order to keep the connectionwith the calling UE, UE may continuously create messages and alsotransmit the messages to the called UE. More specifically, after thecalling UE transmits an invite message or when the calling UE receivesat least one of the following: a 180 ringing message and 100 tryingmessage from the called UE, the calling UE periodically transmits an SIPmessage that does not affect a call setup operation of the called UE tothe called UE. This packet transmission causes the eNB not to releasethe RRC with the calling UE. The packet transmission also causes thecalled UE to process the SIP message transmitted from the calling UE,without altering the call status or the call setting by the SIP message.

FIG. 11 is a signal flow chart that describes a method of continuouslytransmitting messages by UE in order to keep the connection when a VoIMScall setup request is created, according to an embodiment of the presentdisclosure.

Referring to FIG. 11, at least one of the following entities: calling UE1102, eNB 1104, PGW 1106 and called UE 1108 may transmit/receive signalsto/from the other entities.

When a VoIMS call is created, the calling UE 1102 may transmit an invitemessage to the called UE 1108 (1110).

The calling UE 1102 may receive at least one of the following: a 180ringing message and 100 trying message from the called UE 1108 (1115).

The calling UE 1102 may recognize whether a call setting is proceeding(1120). The recognition as to whether a call setting is proceeding maybe determined based on at least one of the messages received inoperation 1115. When the calling UE 1102 recognizes that a call settingis proceeding, the calling UE 1102 may start to periodically create anSIP message and to transmit the SIP message to at least one of thefollowing: the called UE 1108 and a network node including the eNB 1104in order to keep the connection. In the embodiment, the created andtransmitted SIP message may be a message that does not affect a callsetting process. In the embodiment, the SIP message that does not affecta call setting process may be called a dummy SIP message. According toembodiments, the dummy SIP message may include a message, OPTIONS, fordetecting the capability between two entities. The transmission periodof the SIP message may be set in various modes. The SIP message may benon-periodically transmitted.

The SIP message transmitted by the calling UE 1102 may be transmitted tothe called UE 1108 through the network node including the eNB 1104(1125).

The eNB 1104 that receives or transmits a message including the SIPmessage may keep the connection with the calling UE 1102 (1130). Morespecifically, the eNB 1104 may keep the connection with the calling UE1102 by receiving the dummy SIP message from the calling UE 1102.

The calling UE 1102 may receive a 200 OK message, in response to the SIPmessage (e.g., OPTIONS), from the called UE or the network node thatreceived the SIP message (1135).

In the embodiment, the creation and transmission of the dummy SIPmessage by the calling UE 1102 may start: after the calling UE 1102transmits an invite message in operation 1110 and/or after the callingUE 802 analyzes a packet transmitted from the called UE and ascertainsthat at least one of the following: a 180 ringing message and a 100trying message is received. In the embodiment, the calling UE 1102 maytransmit the dummy SIP message after a call has been set up and untilthe call starts, every a period of time or non-periodically. The periodof time may be less than the initial value of the general inactivitytimer of eNB 1104 (e.g., 8 seconds).

For example, after 8 seconds have elapsed from a point in time when thecalling UE 1102 received a 180 ringing message in operation 1115, thecalling UE 1102 may periodically create the dummy SIP message andtransmit the message to at least one of the following: the UE 1108 andthe network node, every 8 seconds.

In addition, the calling UE 1102 may use at least one of the following:an event to receive a 200 OK message in response to the INVITE messagetransmitted from the called UE 1108 and an event to receive a calldecline message from the called party, e.g., an event to receive asignal including a 603 Decline message, as a standard for determining apoint in time when transmission of the message is stopped, (1140). Morespecifically, when the calling UE 1102 receives: the 200 OK message inresponse to the INVITE message from the called UE 1108; or a signalincluding the 603 decline message from the called UE 1108, the callingUE 1102 may stop transmitting the dummy SIP message.

When receiving at least one of the 200 OK message and the call declinemessage, the calling UE 1102 may stop transmitting the dummy SIP message(1145).

Meanwhile, in the embodiment described above or the foregoingembodiments where UE periodically or non-periodically transmits messages(or packets) in order to keep the connection, the transmission period ofpackets by UE may be set to the UE. For example, when eNB on a serviceprovider network sets the initial value of the inactivity timer for UEto 10 seconds, the transmission period of message for keeping theconnection with the UE delivered to the service provider may be to avalue less than the initial value of the timer, e.g., 9 seconds.However, the setting of values of the timer may vary according toembodiments. In order to determine whether to apply the setting, UE mayadditionally determine whether HPLMN (Home PLMN, part of IMSI) of the UEis identical to PLMN of a service provider that is providing services.

As another method, UE may record a point in time that eNB releases theRRC and determine the transmission period of messages to keep theconnection. More specifically, UE may store a time interval from a pointof time that the latest packet was transmitted/received to a point oftime that eNB released RRC connection (or received an RRC connectionrelease message), and may estimate the initial value of the inactivitytimer of the eNB based on the stored time interval. As the methoddescribed above, this method may keep the connection state, every a timeinterval less than the stored time interval, as a period. For example,when the stored time interval, taken to a point in time that RRCconnection is released, is 10 seconds, UE may transmit a message to keepthe connection, once every 9 seconds.

Meanwhile, UE may update a time interval from the latest packettransmission/reception to the RRC release with directionality with thelatest time interval. The time interval may be calculated bycomputational methods such as average or moving average, etc.

Modules or programming modules according to the present disclosure mayinclude one or more components, remove part of them described above, orinclude new components. The operations performed by modules, programmingmodules, or the other components, according to the present disclosure,may be executed in serial, parallel, repetitive or heuristic fashion.Part of the operations can be executed in any other order, skipped, orexecuted with additional operations.

Although exemplary embodiments of the invention have been described indetail above, it should be understood that many variations andmodifications of the basic inventive concept herein described, which maybe apparent to those skilled in the art, will still fall within thespirit and scope of the exemplary embodiments of the invention asdefined in the appended claims.

What is claimed is:
 1. A method of performing transmission/reception ofsignals in an evolved Node B (eNB) of a mobile communication systemcomprising: receiving a first message including service requestinformation from user equipment (UE); transmitting a second messageincluding the service request information to an Mobility ManagementEntity (MME); receiving a third message including context informationfor the UE from the MME; and determining an inactivity timer value forthe UE based on the context information.
 2. The method of claim 1,wherein determining an inactivity timer value comprises: receivingpackets from the UE, based on the context information; and determiningthe inactivity timer value based on an identifier related to a serviceof a bearer transmitting the received packets.
 3. An evolved Node B(eNB) of performing transmission/reception of signals in a mobilecommunication system comprising: a transceiver for performingtransmission/reception of signals; and a controller for: controlling thetransceiver; receiving a first message including service requestinformation from user equipment (UE); transmitting a second messageincluding the service request information to an Mobility ManagementEntity (MME); receiving a third message including context informationfor the UE from the MME; and determining an inactivity timer value forthe UE based on the context information.
 4. The eNB of claim 3, whereinthe controller receives packets from the UE, based on the contextinformation, and determines the inactivity timer value based on anidentifier related to a service of a bearer transmitting the receivedpackets.
 5. User equipment (UE) of performing transmission/reception ofsignals in a mobile communication system comprising: a transceiver forperforming transmission/reception of signals; and a controller forcontrolling the transceiver and transmitting a first message includingservice request information to an evolved Node B (eNB), wherein the eNBdetermines an inactivity timer value for the UE based on contextinformation that is determined according to the service requestinformation.
 6. The UE of claim 5, wherein: the controller transmitspackets to the eNB; and the inactivity timer value for the UE isdetermined based on a bearer through which the packets are transmitted.7. A method of performing transmission/reception of signals in anevolved Node B (eNB) of a mobile communication system comprising:receiving a message for a sending call from calling user equipment (UE);transmitting the message for a sending call to called UE; receiving apacket corresponding to the sending call from the calling UE or a serverrelated to IP Multimedia Subsystem (IMS); and maintaining connectionwith the calling UE based on the received packet.
 8. The method of claim7, further comprising: receiving a response message from the called UE,stopping receiving a packet corresponding to the sending call, based onthe response message.
 9. An evolved Node B (eNB) of performingtransmission/reception of signals in a mobile communication systemcomprising: a transceiver for performing transmission/reception ofsignals; and a controller for: controlling the transceiver; receiving amessage for a sending call from calling user equipment (UE);transmitting the message for a sending call to called UE; receiving apacket for maintaining connection with the calling UE, in response tothe sending call, from the calling UE or a server related to IPMultimedia Subsystem (IMS); and maintaining connection with the callingUE based on the received packet.
 10. The method of claim 9, wherein thecontroller receives a response message from the called UE, and stopsreceiving a packet corresponding to the sending call, based on theresponse message.
 11. User equipment (UE) of performingtransmission/reception of signals in a mobile communication systemcomprising: a transceiver for performing transmission/reception ofsignals; and a controller for: controlling the transceiver; transmittinga message for a sending call to called UE to an evolved Node B (eNB);and transmitting a packet for maintaining connection with the UE, inresponse to the sending call, to the eNB.
 12. The method of claim 11,wherein the controller receives a response message from the called UE,and stops transmitting a packet corresponding to the sending call, basedon the received response message.
 13. An IP Multimedia Subsystem (IMS)related server of performing transmission/reception of signals in amobile communication system comprising: a transceiver for performingtransmission/reception of signals; and a controller for: controlling thetransceiver; receiving a message for a sending call from calling userequipment (UE); transmitting the message for a sending call to calledUE; and transmitting a message for maintaining connection with thecalling UE to the calling UE.
 14. The server of claim 13, wherein thecontroller receives a response message from the called UE, and stopstransmitting a message for maintaining connection with the calling UE,in response to the received response message.